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                [Usaco2017 Open]Switch Grass                </h1>
                <p>时间限制：10s&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;  空间限制：128MB</p>			</div>
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                                <h3>题目描述</h3><p><div>Farmer John has recently been experimenting with cultivating different types of grass on his farm, r</div>
<div>ealizing that different types of cows like different types of grass. However, he must be careful to&nbsp;</div>
<div>ensure that different types of grass are planted sufficiently far away from each-other, in order to&nbsp;</div>
<div>prevent them from being inextricably mixed.FJ's farm consists of Nfields (1&le;N&le;200,000), where M pa</div>
<div>irs of fields are connected by bi-directional pathways (1&le;M&le;200,000). Using these pathways, it is&nbsp;</div>
<div>possible to walk from any field to any other field. Each pathway has an integer length in the range&nbsp;</div>
<div>1&hellip;1,000,000. Any pair of fields will be linked by at most one direct pathway.In each field, FJ init</div>
<div>ially plants one of Ktypes of grass (1&le;K&le;N). Over time, however, he might decide to switch the gra</div>
<div>ss in some field to a different type. He calls this an &quot;update&quot; operation. He might perform several&nbsp;</div>
<div>updates over the course of time, which are all cumulative in nature.After each update, FJ would like</div>
<div>&nbsp;to know the length of the shortest path between two fields having different grass types. That is, a</div>
<div>mong all pairs of fields having different grass types, he wants to know which two are closest. Ideal</div>
<div>ly, this number is large, so he can prevent grass of one type from mixing with grass of another type</div>
<div>. It is guaranteed that the farm will always have at least two fields with different grass types.In&nbsp;</div>
<div>30 percent of the input cases, each field will be directly connected to at most 10 pathways.</div>
<div>
<div>给定一张带权无向图，每个点有一个颜色，每次改变一个点的颜色，要求你在操作后输出这个图中最近异色点对之</div>
<div>间的距离最近异色点对定义为：一对点颜色不同，且距离最小</div>
</div>
<p></p></p><hr/><h3>输入格式</h3><p><div>The first line of input contains four integers, N, M, K, and Q, where Q is the number of updates (1</div>
<div>&le;Q&le;200,000). The next M lines describe the paths; each one contains three integers A, B, and L, in</div>
<div>dicating a path from field A to field B (both integers in the range 1&hellip;N) of length L. The next line</div>
<div>&nbsp;indicates the initial type of grass growing in each field (N integers in the range 1&hellip;K). Finally,&nbsp;</div>
<div>the last Q lines each describe an update, specified by two integers A and B, where the grass in fiel</div>
<div>d A is to be updated to type B</div>
<p></p></p><hr/><h3>输出格式</h3><p><div>For each update, print the length of the shortest path between two fields with different types of grass</div>
<div>
<div>after the update is applied.</div>
</div>
<p></p></p><hr/><h3>样例输入</h3><pre>3 2 3 4
1 2 3
2 3 1
1 1 2
3 3
2 3
1 2
2 2</pre><hr/><h3>样例输出</h3><pre>1
3
3
1
</pre><hr/><h3>提示</h3><p>没有写明提示</p><hr/><h3>题目来源</h3><p>Platinum</p>
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